Electrical precipitation



Filed July '6, 1928 3 SheetSrSheec l 7gb] V NTZF/h f1 498.8% 6384,

ATTORNEYS Oct. 25, 1932. s. P. MILLER ELEGTRICAL PRECIPITATION 3 Sheets-Sheet 2 Filed July 6, 1928 INVENTZB fimi fiww ATTORNEYS Qct. 25, 1932. s. P. MILLER ELECTRICAL PRECIPITATION Filed July 6, 192 8 5 Sheets-Sheet 3 INVENZRM s} J QM I ATTORNEYS Patented Get, 25, 1932 i T E a; T

STUART PARMELEE MILLER, OF ENGLEWOOD, NEW JERSEY, ASSIGNOR TO THE BARRETT COMPANY, OF NEW YORK, N. Y., A CORPORATION OF NEW JERSEY ELECTRICAL PRECIPITATION Application filed. July 6, 1928. Serial. No. 290,852.

This invention relates to the production of pitch and clean gases by cleaning hot coal carbonization gases in an electrical precipitator, and to an improved apparatus which will facilitate such operations.

Electrical precipitators as heretofore used commonly consist of a casing containing a plurality of tubes arranged to convey the gases through the apparatus and havlng electrodes in the tubes. The electrodes are connected normally to the negative terminal of a source of high tension uni-directional current while the tubes are connected usually through the ground to the positive terminals of the source of current. In the operation current is supplied, for example, from an alternating current generator through a transformer and converter and the gas to be cleaned is directed through the tubes and is thus passed through the electrical discharge, Which, by ionization of the particles to be separated, causes them to collect on the Walls of the tubes from which they descend into the bottom of the separator.

According to this invention, the gases undergoing precipitation are maintained at relatively elevated temperatures in the precipitator, so as to retain certain constituents of the gases in the vapor phase. Thus, for example, in the precipitation of tar from cokeoven gases, it is desirable to prevent precipitation of the oil constituents. The dew points of the gases for the several tar and oil constituents are lower than the boiling points thereof. and by properly regulating the temperature of the gases in accordance with the, dew points of the gases for the several constituents, certain constituents may be caused to condense while other constituents are retained in the vapor phase. By proper regulation of the temperature, those constituents, which it is desired to recover as clean oils, are carried thru the precipitator with the gases in vapor form, and they may be recovered 'subof the precipitator and to provide automatic control of the gas temperature.

In carrying out the invention, the precipitator itself may be of the usual or any desired form and construction. It may be provided, for example, with the usual tubes enclosing electrodes connected in the usual way to a source of current. To facilitate operation at elevated temperatures the precipitation zone should be heated. This can be accomplished in various ways. For example, if the precipitator comprises a plurality of tubes enclosing electrodes, the desired temperature can be maintained by circulating a heating medium about the tubes of the precipitator, which may be built into a casing designed for this purpose. The heating medium may advantageously be the hot combustion gases from a gas burner, oil burner, or furnace for the combustion of solid fuel, such as coal, connected directly with the heating jacket.

In the operation of the invention, as described, for the purpose of heating the gases undergoing precipitation, the amount of heat supplied should be regulated in accordance with the particular requirements of the operation, that is to say, to maintain a temperature in the electrical precipitator, which will permit the separation of desired constituents in the precipitator as tar or pitch, while other constituents are retained in the vapor phase and withdrawn with the gases from the precipitator, and later cooled to throw down clean oils. According to this invention, automatic temperature control means is provided for maintaining the. gases leaving the precipitator at a constant temperature. The ordinary type of thermostatic control means may be located in heat exchange relation with the gases leaving the precipitator and so connected that it regulates the amount of heat supplied to the gases by controlling the circulation of the heating medium thru the acket of the precipitator, by controlling the amount of fuel burned to supply combustion gases for the heating jacket, or otherwise regulating the heating of the precipitator by hot gases passing therethru. Where recirculation of the heating gases is employed,

The gases leaving the precipitatorare advantageously kept at such a temperature that the constituents of the gases resulting from the carbonization of coal, which it is desired to recover as clean oils, leave the precipitator in vapor form, so that on cooling, clean oils will be obtained which comprises these constituents, or where a heavy tar or pitch of a particular melting point is desired, the temperature of the gases may be regulated so as to carry from the precipitator those constituents of the coal carbonization gases which it is desired to eliminate from such a tar or pitch. If a pitch of high melting point is desired, a high temperature will be maintained in the precipitator. By maintaining the gases leaving the precipitator at 240 C., in one instance, a large proportion of the oils remained as vapors, and a pitch of a melting point of 265 F., was obtained. At a lower temperature, lower boiling oils will be thrown out in the precipitator, giving a lower melting point pitch, or the temperature may be maintained abovethe dew point of the gases for water but so low that a heavy anhydrous tar will be precipitated. In one case a 250 F. melting point pitch wasobtained by maintaining the gases leaving the preeipitator at 205 C. By providing automatic temperature control, products of uniform composition may be readily obtained with little or no supervision of the precipitator, except that necessary to keep it functioning properly. The heat supplied to the precipitator may be merely that necessary to prevent a drop in the temperature of the gases passing thru the prccipitator, or suflicient heat may be supplied to raise the temperature of the gases slightly. Care must be taken in supplying heat to the gases thru the collecting electrodes in order to prevent carbonization of the tarry and pitchy materials deposited from the gases onto these electrodes.

Fig. 2 is an elevation of the precipitator shown in Fig. 1; and

Figs. 3 and 4: show sections at right angles to one another thru a precipitator of similar structure, with a modified heating arrangement.

Referring to Fig. 1, the gases from the coke ovens 1, pass thru uptake pipes 2, to the collector main 3, supplied with the usual spray means.

Where it is desired to pass the gases thru the precipitator at a high temperature, so that clean oils of more or less high boiling point may be recovered directly from the gases by cooling them, indiscriminate cooling of the gases in the collector main is to be avoided. Thecollector main should be supplied with sufficient liquid to keep it flushed, in order to prevent clogging of the main due to coking of tarry or pitchy material lodged therein. This liquid may, in large part, be flushed in at the end of the main.

The hot gases pass from the collector main thru the cross-over main 4 to the precipitator, an enlarged View of which is shown in Fig. 2. It comprises a shell 5, preferably cylindrical in form, having gas inlet and gas outlet connections 66. The gas to be treated may enter thru the lower port and pass thru the precipitator to the upper port 6, or gas may enter above and pass out thru the lower port; A bafiie 7 is provided, to separate the lower, or liquid collecting chamber 8 from the electrode chamber 9. A plurality of tubes 10 are supported in heads 11 within the electrode chamber and form the positive electrodes of the separator, the shell of which is grounded.

Electrodes 12 are supported thru the bus bar 13 in spaced relation to the walls of the tubes 10. The conducting support extends thru openings 14 into the chambers 15, in which they are supported by insulators 16. Current is supplied to the electrodes thru a conductor 17 from a suitable source of high tension uni-directional current, preferably in the neighborhood of' 35,000 to 50,000 volts.

A combustion chamber 18 is provided and a gas burner 19 is arranged therein, it being understood that the burner is supplied with a combustible gas and a proper quantity of air in the amounts desired and that such a burner is typical of any similar source ofa heating medium, e. g., an oil burner. The combustion gases are delivered to the heating chamber of the precipitator, surrounding the electrodes, e. g., thru .a bustle pipe 20 and t-uyeres 20. The hot gases circulate about the tubes 10 in heat exchange relation with the gases undergoing precipitation. The waste combustion gases are Withdrawn e. g.,

thru the bustle pipe 21 and are delivered to the stack 22 by the pipe 23.

In the operation of the apparatus described, the gases to be cleaned enter thru the inlet 6 at the bottom of the precipitator lil and pass up thru the tubes 10 in which they' are subjected to high tension discharge where solid and liquid particles are removed from the gases. I The treated gases pass out thru the upper port 6. The liquids thrown out of the gas-es may be removed from the bottom of the precipitator thru the outlet 24, continuously or periodically.

in order that the temperature of the gases leaving the precipitator may be kept uniform, thermostatic control means 25 is situated in the gas outlet of the precipitat-or. This control, as shown herein, is connected thru the electric circuit 26 with means 27 which operates the valve 28 and thereby controls the amount of gas supplied to the burner 19. Uther types of thermostatic regulators may be used. The temperature of the gases at the outlet of the precipitator determines to a large extent what condensable constituents will be precipitated in the precipitator and what constituents will be carried thru the precipitator in vapor form. It the gases enter the precipitator at a temperature below that at which it is desired that they should leave, tar or pitch of lower melting point than that desired will be precipitated in the tubes and will be partially distilled by the heat of the hot combustion gases surrounding the tubes. As most of the material entrained in the gases is precipitated at the lower part of the tubes, the length of contact between the precipitated material and the hot tubes is not prolonged. The opportunity for distillation is slight. It constant results are desired, the temperature of gases passed up thru the precipitator should preferably not he more than slightly below the temperature of the gases leaving the precipitator, unless means is provided for heating the gases before they enter the precipitating zone. It the gases are passed down thru the precipitator, suspended particles will be thrown down from the gases onto the collecting electrodes in such a way that most of the material thrown on to the tubes will run down almost the whole height of the tubes, andtherefore, liquids and gases passed down thru the tubes may, when desired, be heated to a considerable extent since tar precipitated from the cooler gases entering the precipitating zone will be distilled in flowing down the tubes and may be brought into equilibrium with the gases of higher temperature as they leave the precipitator. The same precipitator may be used for gases entering the top and leaving the'bottom as for gases entering the bottom and leaving the top. The thermostatic regulator will in each case be located in the outgoing gases.

In some cases it is desirable to have the heating gases and the gases to be heated flowing countercurrent to one another, instead of both passing in the same direction, as described in connection with Figs. 1 and 2.

In Figs. 3 and 4, the heating gases are introduced into the upper end of the acket of the precipitator and pass down thru the jacket and out thru the bottom of the jacket, while the gases to be treated enter at the bottom thru the inlet pipe 30 and pass out thru the outlet pipe 31.

According to the arrangement shown in these figures, the heating ases may be recirculated thru the jacket ot the precipitator. The gases from the combustion chamber 32, which contains the burner 32', enter the jacket of the precipitator thru the bustle pipe 33 and tuyeres 34. The construction of the precipitator shown in Figs. 3 and 4 is similar to that shown in Fig. 2, except for the heatin jacket and connections.

he hot gases pass down around the precipitator tubes and out thru the bustle pipe 35. By adjustment of the dampers-36 and 37, a regulated amount of the hot combustion gases is returned thru the pipe 38 to the combustion chamber 32 by means of the blower 39 operated by the motor 40. The balance of the gases leaving pipe 35 are exhausted thru the stack 41.

By recirculation of the heating gases, the velocity at which the gases pass thru the jacket of the precipitator is increased. There is less likelihood of pockets oi gas forming in regions not in direct line with the main flow of the gas thru the precipitator jacket,

and more eiiicient heat transfer between the hot gases and the tubes is possible. Another important feature of the recirculation of the heating gases depends upon the fact that the heating eificiency of gases circulating thru the jacket of any apparatus is dependent upon the temperature drop between the gases adjacent to the inner and outer walls of the device containing the gases to be heated, in this case, the precipitator tubes. By recirculating the gases and increasing the velocity at which they pass thru the jacket, the temperature drop between the outer wall of the tubes and the gases passing around the tubes is kept at or near the maximum possible.

The gases to be treated pass up thru the apparatus shown in Figs. 3 and 4. Solid and liquid particles are thrown out ofthe gases due to the high tension discharge between the electrodes and the walls of the tubes 10. The heatinggases pass down around the tubes at high velocity. Due to the high velocity and countercurrent flow of the gases to be heated and the heat-ing gases, the heating eiiiciency of theapparatus shown is high.

The temperature of the gases leaving the precipitator will be so regulated that a tar or pitch of desired composition Wlll be thrown down in the precipitator, and desired oils will be carried by the clean gases from the precipitator in vapor form. These oil vapors may be recovered as clean oils, by cooling in condensers, such as those shown at llllt) 45 and 46 in Fig. 1. One or more clean oil fractions may be recovered. An exhauster 47 is shown for drawing the gases thru the system.

I claim:

1. The method of Operating electrical precipitators which comprises passing a gas thru precipitator tubes containing a discharge electrode, burning combustible material in a chamber connected with a jacket around the precipitator tubes, circulatin the hot combustion gases through the jac et around the precipitator tubes, and recirculating a portion of the combustion gases leaving the jacket of the precipitator thru the said jacket together with fresh hot combustion gases.

2. A method of cleaning gases and vapors by electrical precipitation while controlling the temperature of the gases and vapors being cleaned, which comprises passing the gases and vapors thru an electrical precipitator, subjecting them therein to an electrical discharge, passing a medium of different temperature from the gases and vapors in heat interchange relation with the gases and vapors, passing the gases and vapors in heat interchange relation with thermostatic con trol means, and thereby controlling the tem-- perature of the medium passed in heat interchange relation with the gases and vapors.

3. An electrical precipitator comprising means for conveying a gas thru the precipitating zone thereof, a heating jacket in heat interchange relation with said means, and a combustion chamber adjacent to said heating jacket with means for supplying hot combustion gases of regulated temperature from the combustion chamber to the heating jacket so as to bring them into heat interchanging relation with the gas being subjected to elec trical precipitation.

4. An electrical precipitator comprising means for conveying a gas thru the precipitating zone thereof, a heating jacket in heat interchange relation with said means, a combustion chamber adjacent to said heat ng jacket with means for supplying hot combustion gases to the heating jacket, means for removing combustion gases which have passed into heat interchange relation wlth the gases to be precipitated, and means for recirculating a portion of these gases by again bringing them into heat interchange relation with the gases to be treated.

5. An electrical pre'cipitator comprising precipitator tubes thru which the gases to be treated are passed, a jacket surrounding the electrode tubes, a combustion chamber in proximity to said acket, means for conveying combustion gases from said combustion chamber to the jacket, and means for recirculating a portion of the gases leaving the precipitator jacket by conveying them into the combustion chamber.

6. An electrical precipitator for treating gases comprising a passage for the ases to be treated, means for causing an e ectrical discharge therein, means for circulating a heating medium in heat interchange relation with the gases to be'treated and thermostatic control means situated at the outlet of the be treated, means for causing an electrical discharge therein, means for circulating a heating medium in heat interchange relation with the gases to be treated and thermostatic control means situated at the outlet of the passage for the gases to be treated, said control means being operatively connected with means for controlling the temperature of the heating medium.

8. An electrical precipitator for cleaning gases comprising collecting electrode tubes with discharge. electrodes passing therethru, a heating jacket surrounding the tubes, a combustion chamber with a burner therein in direct communication with the heating jacket, thermostatic control means adapted to be actuated by the cleaned gases as they leave the precipitator, and electric means connect ed therewith for controlling the supply of fuel to the burner.

9. The method of operating electrical precipitators in the treatment of coke oven gases which comprises passing fresh tar laden coke oven gases through the precipitating zone of an electrical precipitator, supplying heat to the gases and maintaining these gases while passing through the precipitating zone at a substantially iiniform terperature lower than that at which they left the coke ovens but sufliciently high to maintain oils therein in vapor form and maintaining an electrical discharge in the precipitating zone so as to,

remove entrained pitch particles from the gases.

10. The method of operating electrical precipitators in the treatment of coke oven gases which comprises passing fresh tar laden coke oven gases through the precipitating zone of an electrical precipitator, supplying heat to the gases and maintaining these gases while passing through the precipitating zone at a substantially uniform temperature above the dew point of the gases for water but lower than that at which they left the coke ovens and maintaining an electrical discharge in the precipitating zone so as to remove entrained pitch particles from the gases.

11. The method of operating electrical precipitators in the treatment of coke oven gases which comprises passing fresh tar laden coke oven gases through the precipitating neeeoee zone of an electrical precipitator, supplying heat to the gases and maintaining them While passing through the precipitating zone at a substantially uniform temperature of at least 205 C. but flower than the temperature at which they left the ovens and maintaining an electrical discharge in the precipitating zone so as to remove entrained pitch particles from the gases.

In testimony whereof I afix my signature.

STUART PARMELEE MILLER, 

